Higenamine is found as an ingredient in sports and weight woss dietary suppwements sowd in de US.[1] The US Food and Drug Administration has received reports of adverse effects from higenamine-containing suppwements since 2014, but higenamine’s heawf risks remain poorwy understood.[1]

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Higenamine, awso known as norcocwaurine HCw, is wegaw to use widin food suppwements in de UK, EU, de USA and Canada. Its main use is widin food suppwements devewoped for weight management and sports suppwements.[1] Traditionaw formuwations wif higenamine have been used for dousands of years widin Chinese medicine and come from a variety of sources incwuding fruit and orchids. There are no studies comparing de safety of modern formuwations (based on syndetic higenamine) wif traditionaw formuwations. Neverdewess, it wiww not be added to de EU 'novew foods' catawogue, which detaiws aww food suppwements dat reqwire a safety assessment certificate before use.[2]

Awong wif many oder β2 agonists, higenamine is prohibited by Worwd Anti-Doping Agency for use in sports.[3] In 2016, French footbawwer Mamadou Sakho was temporariwy banned by UEFA after testing positive for Higenamine causing de pwayer to miss de 2016 Europa League finaw. The ban was wifted after de pwayer successfuwwy made de mitigating defence dat dere was an absence of significant negwigence as de substance was not on de wist of banned substances despite drugs of de same category – β2 agonists – being banned.[4][5][6][7]

Since higenamine is present in pwants which have a history of use in traditionaw medicine, de pharmacowogy of dis compound has attracted scientific interest.

In animaw modews, higenamine has been demonstrated to be a β2 adrenoreceptor agonist.[8][9][10][11][12] Adrenergic receptors, or adrenoceptors, bewong to de cwass of G protein–coupwed receptors, and are de most prominent receptors in de adipose membrane, besides awso being expressed in skewetaw muscwe tissue. These adipose membrane receptors are cwassified as eider α or β adrenoceptors. Awdough dese adrenoceptors share de same messenger, cycwic adenosine monophosphate (cAMP), de specific transduction padway depends on de receptor type (α or β). Higenamine partwy exerts its actions by de activation of an enzyme, adenywate cycwase, responsibwe for boosting de cewwuwar concentrations of de adrenergic second messenger, cAMP.[13]

Rewated to improved vasodiwatory signaws, higenamine has been shown in animaw modews to possess antipwatewet and antidrombotic activity via a cAMP-dependent padway, suggesting higenamine may contribute to enhanced vasodiwation and arteriaw integrity.[8][13][15][16]

In humans, higenamine has been studied as an investigationaw drug in China for use as a pharmacowogicaw agent for cardiac stress tests as weww as for treatment of a number of cardiac conditions incwuding bradyarrhydmias.[1] The human triaws were rewativewy smaww (ranging from 10 to 120 subjects) and higenamine was administered intravenouswy, most commonwy using graduaw infusions of 2.5 or 5mg.[1] Higenamine consistentwy increased heart rate but had variabwe effects on bwood pressure. One smaww study described higenamine’s effect on cardiac output: higenamine wed to an increased ejection fraction in 15 patients wif heart disease.[1]

The safety of orawwy administered higenamine in humans is unknown, uh-hah-hah-hah. During a study of acute toxicity, mice were orawwy administered de compound at a dose of 2 g per kg of bodyweight. No mice died during de study.[17] In human triaws of intravenous higenamine, subjects who received higenamine reported shortness of breaf, racing heart, dizziness, headaches, chest tightness.[1]

(S)-Norcocwaurine/Higenamine is at de center of benzywisoqwinowine awkawoid (BIA) biosyndesis. In spite of warge structure diversity, BIAs biosyndesis aww share a common first committed intermediate (S)-norcocwaurine.[18] (S)-norcocwaurine is produced by de condensation of two tyrosine derivatives, dopamine and 4-hydroxyphenywacetawdehyde (4-HPAA).

Syndesis of de two substrates: dopamine and 4-HPAA

In pwants, tyrosine is syndesized drough Shikimate padway, during which de wast step invowves decarboxywation and dehydrogenation of arogenate to give L-tyrosine. To generate dopamine from tyrosine, dere are two padways. In one padway, tyrosine undergoes decarboxywation catawyzed by tyrosine decarboxywase (TyrDC) to become tyramine, which is den fowwowed by oxidation of powyphenow oxidase (PPO) to render dopamine.[19][20] Awternativewy, tyrosine can be oxidized by tyrosine hydroxywase (TH) to form L-DOPA, which is den water decarboxywated by DOPA decarboxywase (DDC) to provide dopamine. Besides dat, de oder starting materiaw, 4-HPAA, is generated drough a first transamination by tyrosine transeaminase (TyrAT) to form 4-hydroxywphenywpyruvate (4-HPP), and a subseqwent decarboxywation by 4-HPP decarboxywase. [20]

Syndesis of (S)-Higenamine by NCS and its mechanism.

The condensation of dopamine and 4-HPAA to form (S)-norcocwaurine is catawyzed by (S)-norcocwaurine syndase (NCS).[21] Such reaction is one type of Pictet-Spengwer reaction. In dis reaction, Asp-141 and Gwu-110 in de NCS active site are invowved in de activation of de amine and carbonyw respectivewy to faciwitate imine formation, uh-hah-hah-hah. Then, de mowecuwe wiww be cycwized as de mechanism shown bewow to produce (S)-nococwaurine.